Generally, window panes protect the interior of rooms from influences of the variable external atmosphere, e.g. from seasonal varying temperatures, emissions of noise, exhaust gas and dust and, moreover, are expected to transmit a sufficient amount of daylight for an adequate room illumination. With the daylight--consisting of direct and diffuse solar radiation--energy penetrates the windows which contributes to the heating of the interior of rooms. In winter this heat gain--as far as glare can be avoided or is experienced as non-disturbing, respectively,--generally is desirable, whereas in summer the heating of rooms by solar irradiation generally is undesirable.
The glazing of openings in buildings is commonly performed by isolating glass panes consisting of two or more plane sheets of glass which influence the thermal balance and, hence, the interior climate of the buildings. Isolating glass panes essentially transmit direct and diffuse solar light in order to provide luminous room interiors during daytime. In order to limit the heat flow into rooms caused by solar irradiation, the transmittance of isolating glass panes is reduced by providing a reflective layer on one face of a glass sheet. By this means, however, the illumination of the rooms is reduced, too.
A non-movable, vertical pane based on the optical properties of prisms is known which rejects the direct solar radiation in summer and reasonably transmits the direct solar radiation in winter (French patent application no. 8017364 from 1980, publication no. 2463254). A sheet of transparent material with a prismatic structure consisting of horizontal ribs and grooves of triangular cross-section pointing away from the building is employed. The function of this prismatic pane bases upon the total internal reflection of direct solar radiation occuring at the plane face pointing to the building for solar altitudes above a certain limiting angle. An equation is presented which relates the the limiting angle of the solar altitude, the critical angle of incidence at which a ray impinging internally on the plane face is just totally reflected and the angle between the upper surface of the prismatic rib and the vertical with each other. Prismatic panes of this kind have the disadvantage that they provide the intended total rejection of direct sunlight only for orientations of the pane narrow to the south and only for a limited time period during summer. These limitations are deemed to be the essential reasons for the fact that this prismatic pane is scarcely applied in practice.
Another pane is known which is suitable as an optical component for use in glazing (international patent application no. PCT/GB94/00949 from 1994, international publication no. WO94/25792). It comprises two transparent, substantially plane elements each having a plurality of horizontal grooves of adequately shaped cross-sections. This invention intends to provide an optical component which enhances the illumination by daylight within a building interior and nevertheless allows an almost normal, undistorted view from inside a building through the window. Although one embodiment of this invention is designed for protecting against direct solar irradiation, this invention obviously cannot simultaneously solve the main tasks mentioned above and provide protection against solar heat flow into rooms. The influence of different window orientations is not taken into account.